Abstract
Due to tetracycline abuse, the safe bifidobacteria in the human gastrointestinal intestinal tract (GIT) may serve as a reservoir of tetracycline resistance genes. In the present investigation of 92 bifidobacterial strains originating from the human GIT, tetracycline resistance in 29 strains was mediated by the tet(W), tet(O) or tet(S) gene, and this is the first report of tet(O)- and tet(S)-mediated tetracycline resistance in bifidobacteria. Antibiotic resistance genes harbored by bifidobacteria are transferred from other bacteria. However, the characteristics of the spread and integration of tetracycline resistance genes into the human intestinal bifidobacteria chromosome are poorly understood. Here, conserved sequences were identified in bifidobacterial strains positive for tet(W), tet(O), or tet(S), including the tet(W), tet(O), or tet(S) and their partial flanking sequences, which exhibited identity with the sequences in multiple human intestinal pathogens, and genes encoding 23 S rRNA, an ATP transporter, a Cpp protein, and a membrane-spanning protein were flanking by the 1920-bp tet(W), 1920-bp tet(O), 1800-bp tet(O) and 252-bp tet(S) in bifidobacteria, respectively. These findings suggest that tetracycline resistance genes harbored by human intestinal bifidobacteria might initially be transferred from pathogens and that each kind of tetracycline resistance gene might tend to insert in the vicinity of specific bifidobacteria genes.
Highlights
There are up to 1013–1014 total bacteria in the human gastrointestinal intestinal tract (GIT)[1, 2]
Because bifidobacteria are ingested as probiotics in the human GIT and have acquired a “generally regarded as safe” (GRAS) status[7,8,9], so far, only tet(W)- and tet(M)-mediated tetracycline resistance have been detected in intestinal bifidobacteria of human origin[10,11,12,13], and only tet(L), tet(O/W), tet(W/32/O), and tet(O/W/32/O/W/O)-mediated tetracycline resistance have been detected in intestinal bifidobacteria of pig origin[14]
Twenty-nine bifidobacterial strains, including the seven Bifidobacterium longum strains shown in Table 1 and two Bifidobacterium bifidum strains, six Bifidobacterium pseudocatenulatum strains, 13 Bifidobacterium lactis strains and one Bifidobacterium breve strain shown in Table 2, exhibited strong tetracycline resistance [minimum inhibitory concentration (MIC) ≥256 μg/ml], with MIC values that higher than the breakpoint for Bifidobacterium defined by the European Food Safety Authority (EFSA) (MIC = 8 μg/ml)[16]
Summary
There are up to 1013–1014 total bacteria in the human gastrointestinal intestinal tract (GIT)[1, 2]. It remains unknown whether tetracycline resistance genes other than tet(W) and tet(M) can be detected in the bifidobacterial strains originating in the human GIT.
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